<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- This file documents the BFD library.

Copyright (C) 1991-2017 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "GNU General Public License" and "Funding
Free Software", the Front-Cover texts being (a) (see below), and with
the Back-Cover Texts being (b) (see below).  A copy of the license is
included in the section entitled "GNU Free Documentation License".

(a) The FSF's Front-Cover Text is:

A GNU Manual

(b) The FSF's Back-Cover Text is:

You have freedom to copy and modify this GNU Manual, like GNU
     software.  Copies published by the Free Software Foundation raise
     funds for GNU development. -->
<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
<head>
<title>Untitled Document: Section Output</title>

<meta name="description" content="Untitled Document: Section Output">
<meta name="keywords" content="Untitled Document: Section Output">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link href="index.html#Top" rel="start" title="Top">
<link href="BFD-Index.html#BFD-Index" rel="index" title="BFD Index">
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="Sections.html#Sections" rel="up" title="Sections">
<link href="typedef-asection.html#typedef-asection" rel="next" title="typedef asection">
<link href="Section-Input.html#Section-Input" rel="prev" title="Section Input">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.indentedblock {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
div.smalllisp {margin-left: 3.2em}
kbd {font-style:oblique}
pre.display {font-family: inherit}
pre.format {font-family: inherit}
pre.menu-comment {font-family: serif}
pre.menu-preformatted {font-family: serif}
pre.smalldisplay {font-family: inherit; font-size: smaller}
pre.smallexample {font-size: smaller}
pre.smallformat {font-family: inherit; font-size: smaller}
pre.smalllisp {font-size: smaller}
span.nocodebreak {white-space:nowrap}
span.nolinebreak {white-space:nowrap}
span.roman {font-family:serif; font-weight:normal}
span.sansserif {font-family:sans-serif; font-weight:normal}
ul.no-bullet {list-style: none}
-->
</style>


</head>

<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
<a name="Section-Output"></a>
<div class="header">
<p>
Next: <a href="typedef-asection.html#typedef-asection" accesskey="n" rel="next">typedef asection</a>, Previous: <a href="Section-Input.html#Section-Input" accesskey="p" rel="prev">Section Input</a>, Up: <a href="Sections.html#Sections" accesskey="u" rel="up">Sections</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="BFD-Index.html#BFD-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Section-output"></a>
<h4 class="subsection">2.6.2 Section output</h4>
<p>To write a new object style BFD, the various sections to be
written have to be created. They are attached to the BFD in
the same way as input sections; data is written to the
sections using <code>bfd_set_section_contents</code>.
</p>
<p>Any program that creates or combines sections (e.g., the assembler
and linker) must use the <code>asection</code> fields <code>output_section</code> and
<code>output_offset</code> to indicate the file sections to which each
section must be written.  (If the section is being created from
scratch, <code>output_section</code> should probably point to the section
itself and <code>output_offset</code> should probably be zero.)
</p>
<p>The data to be written comes from input sections attached
(via <code>output_section</code> pointers) to
the output sections.  The output section structure can be
considered a filter for the input section: the output section
determines the vma of the output data and the name, but the
input section determines the offset into the output section of
the data to be written.
</p>
<p>E.g., to create a section &quot;O&quot;, starting at 0x100, 0x123 long,
containing two subsections, &quot;A&quot; at offset 0x0 (i.e., at vma
0x100) and &quot;B&quot; at offset 0x20 (i.e., at vma 0x120) the <code>asection</code>
structures would look like:
</p>
<div class="example">
<pre class="example">   section name          &quot;A&quot;
     output_offset   0x00
     size            0x20
     output_section -----------&gt;  section name    &quot;O&quot;
                             |    vma             0x100
   section name          &quot;B&quot; |    size            0x123
     output_offset   0x20    |
     size            0x103   |
     output_section  --------|
</pre></div>

<a name="Link-orders"></a>
<h4 class="subsection">2.6.3 Link orders</h4>
<p>The data within a section is stored in a <em>link_order</em>.
These are much like the fixups in <code>gas</code>.  The link_order
abstraction allows a section to grow and shrink within itself.
</p>
<p>A link_order knows how big it is, and which is the next
link_order and where the raw data for it is; it also points to
a list of relocations which apply to it.
</p>
<p>The link_order is used by the linker to perform relaxing on
final code.  The compiler creates code which is as big as
necessary to make it work without relaxing, and the user can
select whether to relax.  Sometimes relaxing takes a lot of
time.  The linker runs around the relocations to see if any
are attached to data which can be shrunk, if so it does it on
a link_order by link_order basis.
</p>

<hr>
<div class="header">
<p>
Next: <a href="typedef-asection.html#typedef-asection" accesskey="n" rel="next">typedef asection</a>, Previous: <a href="Section-Input.html#Section-Input" accesskey="p" rel="prev">Section Input</a>, Up: <a href="Sections.html#Sections" accesskey="u" rel="up">Sections</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="BFD-Index.html#BFD-Index" title="Index" rel="index">Index</a>]</p>
</div>



</body>
</html>
